1. Field of the Invention
The present invention relates to a display device displaying images by current-driving a light emitting element arranged at each pixel. The invention also relates to an electronic product using the display device. Particularly, the invention relates to a drive system of a so-called active matrix display device, which controls a current amount flowing in the light emitting element such as an organic EL element by an insulated-gate field effect transistor provided in each pixel circuit.
2. Description of the Related Art
In display devices, for example, in a liquid crystal display, a large number of pixels are arranged in a matrix state and images are displayed by controlling transmission intensity or reflection intensity of incident light in each pixel in accordance with image information to be displayed. This is the same as in an organic EL display in which organic EL elements are used for pixels, however, the organic EL element is a self-luminous element which is different from a liquid crystal pixel. Accordingly, the organic EL display has advantages, for example, visibility of images is higher, a backlight is not necessary and response speed is higher as compared with the liquid crystal display. Additionally, the luminance level (gray scale) of each light emitting element can be controlled by a current value flowing in each element, and the organic EL display is largely different from the liquid crystal display which belongs to a voltage control type in a point that it belongs to a so-called current control type.
The organic EL display has a passive matrix type and an active matrix type as a drive system thereof in the same manner as the liquid crystal display. The former has problems such that it is difficult to realize a large-sized as well as high-definition display though the structure is simple, and therefore, the active matrix type is extensively developed at present. In this type, electric current flowing in the light emitting element in each pixel circuit is controlled by an active element (commonly, a thin-film transistor, TFT) provided in the pixel circuit, which is written in the following Patent Documents.    [Patent Document 1] JP-A-2003-255856    [Patent Document 2] JP-A-2003-271095    [Patent Document 3] JP-A-2004-133240    [Patent Document 4] JP-A-2004-029791    [Patent Document 5] JP-A-2004-093682    [Patent Document 5] JP-A-2006-215213